Embedding LateX code into markups

[Walter Hofmeister]

Lilypond 2.2.5 on Mac OS X 10.3.4

Hello. I am trying make up an indication for Classic Guitar Barre and
half-barre indications. For the full barre I am using:
 \markup { \bold \large { C } } and for half-barre:
 \markup { \bold \large { 1/2C } }. These work OK but I would like to
type-set the fraction like a mathematical 1/2 instead of a text one. I have
tried \markup { \bold \large { \\$\frac{1}{2}$CIII } } and other variations
but none seem to work. Could someone tell me how this might be done? Thanks.

Walter Hofmeister